This invention generally relates to a fluid power and control system, in which the exhaust flow of system motors is used directly to provide inlet flow requirement of the system pump.
In still more particular aspects this invention relates to pressurized exhaust system of a plurality of fluid motors, controlled by load responsive valves, the exhaust system supplied with a make-up and fluid exchange pump and used to supply the inlet flow requirements of the system pump.
In still more particular aspects this invention relates to a load responsive fluid power and control system in which the exhaust flow of system motors, supplemented by fluid flow from a make-up and fluid exchange pump, equipped with load responsive unloading and bypass device, is used to supply pressurized inlet flow requirement of the system pump.
Pressurization of the exhaust flow from compensated load responsive valves and also pressurization of system pump inlet is very desirable, but it suffers from the disadvantage of comparatively large throttling losses, directly affecting system efficiency and from the necessity of providing full flow inlet pressurizing pump which is expensive. Closed loop systems, involving a pump and a rotary type fluid motor are well known in the art. Such closed loop systems are characterized by their pressure flow being approximately equal to their exhaust flow. A small exhaust feeding or make-up pump is usually provided to pressurize the exhaust loop and to provide a measure of fluid exchange, in order to cool the closed loop system. Such a make-up pump supplies full flow of pressurized fluid in system standby condition and is not intended for systems, in which comparatively large differences between pump outlet flow and system return flow can take place, which is the case in systems using cylinders as fluid motors. Full flow inlet pressurization has been used in the past, but as previously mentioned it is expensive, since it requires not only a full flow low pressure make-up pump, but also separate drive, large fluid lines, fittings etc.